[ADT] Fix iplist_impl - use after move warnings (PR43943)

As detailed on PR43943, we're seeing static analyzer use after move warnings in the iplist_impl move constructor/operator as they call std::move to both the TraitsT and IntrusiveListT base classes.

As suggested by @dexonsmith this patch casts the moved value to the base classes to silence the warnings.

Differential Revision: https://reviews.llvm.org/D74062